Paraskevidekatriaphobia: Fear of Friday the 13th
I have before me the abstract of a study published in the British Medical Journal in 1993, entitled "Is Friday the 13th Bad for Your Health?" With the aim of mapping "the relation between health, behaviour, and superstition surrounding Friday 13th in the United Kingdom," its authors compared the ratio of traffic volume to vehicular accidents on two different days, Friday the 6th and Friday the 13th, over a period of years.
Surprisingly, they found that in the region sampled, while consistently fewer people chose to drive on Friday the 13th, the number of hospital admissions due to accidents was significantly higher than on "normal" Fridays.
Their conclusion:
"Friday 13th is unlucky for some. The risk of hospital admission as a result of a transport accident may be increased by as much as 52 percent. Staying at home is recommended."
Paraskevidekatriaphobics — people afflicted with a morbid, irrational fear of Friday the 13th — are no doubt pricking up their ears just now, buoyed by evidence that their fears may not be so irrational after all. But it's unwise to take solace in a single scientific study (the only one of its kind, so far as I know), especially one so peculiar. I suspect it has more to teach us about human psychology than it does about any particular date on the calendar.
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http://urbanlegends.about.com/cs/historical/a/friday_the_13th.htm